This is the software that I use regularly and strongly recommend. I've also sprinkled a few discussion groups and software sources as well.
This is all Macintosh software. While I’m a strong proponent of buying a computer based on whether or not it does the job for you, let me recommend that you get a Macintosh if you want to serve to the net. You’ll spend a lot more time putting up content and a lot less time mucking around the system. This is from a person who has used a large number of different computers as personal computers and as servers.
GIMP, Inkscape, and Scribus
They’re also very useful if you’re planning on letting other people improve on your designs. Inkscape’s native format is SVG, and it can easily save in the standard SVG format for other drawing applications. All three of them are freely available, which means that if you make your documents available in those formats, anyone can go ahead and download the software package necessary to edit them.